late breaking news. Now we turn to the george zimmerman trial, the prosecution trying to raise doubt about his claim of self-defense about the night trayvon martin was killed. Today the issue, how serious were the injuries zimmerman sufrpd in the encounter. Matt gutman has more from the courtroom. Reporter: The prosecution trying to punch its way out of a corner. I'm hitting you, correct? Yes. Reporter: The prosecutor hacking into zimmerman's claim of self-defense. That's what the defendants is claiming. Would you have your hands like that, like this or would you be fighting me? I'd be fighting you. Reporter: Swinging for one of the key clauses defining second degree murder, ill will and spite, using zimmerman's own words from that night. They always get away. In your opinion calling somebody referencing them as -- pardon me language as punks? This is ill will. Reporter: The state called a medical examiner who said his head may have been only slammed into the concrete once. He told police he had been struck up to 30 times. The injuries on the back of the defendant's head consistent with one strike against a concrete surface? Yes. Reporter: Moments ago we spoke with zimmerman's lead attorney. He t us to prove self-defense zimmerman doesn't have to show any visible injure ice. All he has to prove is that he reasonably feared for his life. Chief legal correspondent and "nightline" anger, dan abrams will be live in florida tonight, a special edition of "nightline" coming up tonight.

This transcript has been automatically generated and may not be 100% accurate.

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